Storage tube



L. PENSAK STORAGE TUBE Dec. 20, 1955 2 Sheets-Sheet 1 Filed Deo. l 1951ORNEY INVENTOR UU/5' Pf/vSA/f @n ummm* mbw EG SSS@ L. PENSAK STORAGETUBE Dec. 20, 1955 Filed Dec. 1, 1951 2 Sheets-Sheet 2 i/ 7741/6 5665EA/(Mfr/1L) Bmw/V6 SceffA/ (META L) /EL 50m/c sf/ff l/V TIL/[ORDER 0F 5MILS INVENTOR LDU/5 FEA/SAK ORNEY United States Patent "O STORAGE TUBELouis Pensak, Princeton, N. J., assignor to Radio Corporation ofAmerica, a corporation of Delaware Application December 1, 1951, SerialNo. 259,344

7 Claims. (Cl. S15-{L6} This invention is directed to an electrondischarge device and, more particularly, to a storage tube for thepurpose of storing signals of variable intensity, which can be used toproduce output signals corresponding to those stored.

A storage tube is one which can be used for applications in which it isdesired to store signals of variable intensity in an arbitrary scanningpattern and produce output signals proportional to those stored. Onetype of storage tube is that disclosed in my copending applicationSerial Number 29,746, iiled May 28, 1948, now abandoned and assigned tothe same assignee as the present invention. This tube has a dielectrictarget elec` trode formed of an insulating sheet of material and uponwhich is established a pattern of charges. The charge pattern isproduced on one surface by scanning the dielectric target with a beam ofelectrons, which is modulated by incoming signals. Because `of theinsulating nature of the target sheet, the charge pattern remains on thetarget for a period of time. During this time the target surface isscanned by a second beam of electrons to produce a variable secondary`electron emission from the charged target surface, which is collected toproduce an output signal of the tube. The output signals may be producedby a different scanning pattern than that by which the charged patternwas established on the target.

ln a storage tube of the type described above, it is desirable that itbe possible to obtain many copies of the output signal. Also it isdesirable that such a tube resolve half-tone signals lying between themaximum and minimum signals applied to the tube. An example of such anapplication would be in the reception of radar signals from an airplanebehind a cloud. The signal from the airplane will be stronger than thatfrom the cloud itself. In this application, it is desirable that thesignal from the airplane be not lost because of the simultaneous signalfrom the cloud. It is desirable, therefore, to be able to store bothsignals andto be able to distinguish between the signals from the cloudand from the airplane.

lt is, therefore, an object of this invention to provide an improvedcharge` storage tube in which it iS possible to obtain many copies ofthe output signal from a single stored pattern. v

lt is another object of my 4invention to provide an improved chargestorage tube, in which it is possible 4 to resolve half-tone signals forvarious applications.

It is another object of my invention to provide an improved storage tubecapable of receiving, storing, `and regenerating electric signalswithout loss ofl half-tone values. 3

It is a further object of my invention to provide an improved chargestorage tube, 4which can store signals oi varying intensity andreproduce them as television signals without loss of intensity values,and for a large number of copies. i l

My invention is specifically directed to a charge stor- 2,728,020Patented Dec. 20, 1955 age tube having a thin dielectric target sheet.An electron gun means is arranged to produce and scan one surface of thedielectric target sheet with a beam of low velocity electrons. A secondelectron gun, positioned on the opposite side of the target from the rstgun, is used to scanthe opposite surface of the dielectric target sheetwith a beam of high velocity electrons. On the first surface of thedielectric sheet, there is formed a ne mesh grid used as a collectorelectrode for the low velocity beam electrons. Closely spaced from theopposite surface of the dielectric target sheet, is a suppressor screenor grid. Incoming signals are used to modulate the high velocityelectron beam, which strikes the dielectric target to produce asecondary electron emission therefrom. 'I'he suppressor screen isoperated at a low negative potential to drive most of these secondaryelectrons back to the target surface, whereby a negative charge patternis established on the target surface in accordance with the modulatedbeam scanned over the target. The negative charges of the patternestablish a corresponding negative field on the other surface of thedielectric sheet to control the landing of the low velocity beam uponthe positive collector grid on the target surface. The number ofelectrons which land on the collector grid from the low velocity beam isinversely proportional to the negative potential iield at each point.The electrons of the low velocity beam not landing on thecollectorelectrode are returned to an anode collector electrode to form theoutput signal of the tube. Figure l is a sectional view of a chargestorage tube in accordance with my invention. Figure 2 is a greatlyenlarged partial sectional View of the Atarget used in the tube ofFigure l.

Figure 3 is a schematic showing of the conditions at the target duringthe operation of the tube of Figure l. Figure 4 is a graphical showingof the conditions at the target during the operation of the tube ofFigure l. The tube shown in Figure l has an evacuated envelope 10 ofsubstantially tubular conguration. Mounted in the center portion ofthetube is a target electrode 12, consisting principally of a dielectricsheet 14 mounted transversely to the axis of the tube envelope. ,On' oneside of the target electrode 12, there is positioned an electron gunstructure 16, which is used to establish on the adjacent surface ofdielectric sheet 14, a charge pattern. Electron gun 16 may also bereferred to as the "Writing gun. Gn the opposite side of target l2 andcoaXially aligned with the Writing gun 16, there is a second electrongun 1S for providing a low velocity electron beam 20, which is scannedover the adjacent surface of target 12. The low velocity beam Zti ismodulated by the charge pattern established by the writing gun on theopposite target surface to provide the output signal of the tube.Electron gun 18 is also considered the reading gun of the tube.

The writing gun 16 is of a conventional type and consists of'principally a tubular cathode 22 having a closed end portion facingtarget 12, which is coated in a Wellknown manner by a mixture ofstrontium and barium oxides to provide a source of electrons. Enclosingcathode 22 is a tubular control grid 24 having an apertured wall portion23 overlying the activated cathode surface. Coaxially aligned with thecathode 22 and control grid 24- are mounted in a spaced relationship, `ascreen grid electrode 26 and a tubular accelerating electrode 28, eachhaving `openings therethrough for the passage 'of electrons fromcathode'22 to screen l2;

,The gun l16 forms the electrons from cathode 22 into an electron beam2'7jwhich is accelerated toward the target 12. A second acceleratingelectrode 3@ is formed as `a conductive wall coating on the innersurface of the tube envelope and is operated at a higher positivepotential than the iirst accelerating electrode 28 to providetherebetween a focussing eld for bringing the electrons of beam 27 to asmall well-defined spot on the surface of target 12. Electron beam27visy scanned over the surface of target 12 in any well-known manner,such as by magnetic scanning fields provided by two pairs of coilsmounted around the tubular envelope as a neck yoke 32. If the writinggun 16 is used with radar signals, the deflection yoke 32 may be of thetype to produce a radar P. P. I. scan pattern. Such a scansion iswellknown and is also discolsed in U. S. Patent 2,412,670. Figure 1indicates voltage values which may be applied to the several electrodesof the writing gun 16. vThese are by way of example only and are notlimiting. I

The reading gun 18 is of the type used in the Image Orthicon pickup tubeand is disclosed in greater detail in U. S. Patent 2,540,621 to Ralph E.Johnson. The gun consists primarily of a cathode, a control grid (bothnot shown), a first accelerating electrode 34, and a second acceleratingelectrode consisting of a conductive wall coating 36. When appropriatevoltages are applied to the several electrodes of the reading gun, theelectron emission from the cathode is formed into an electron beam 20. Amagnetic focussing field is provided by a coil 38 between theaccelerating electrode 34 and target 12 to focus the electrons of beam20 to a well defined point on the surface of the target 12.

The dielectric target sheet 14 may be of 'a thin sheet of mica or a iilmof glass having a resistivity in the range between 1014 ohm centimetersand 101s ohm centimeters. On the surface of the dielectric sheet 14facing the reading gun 18, there is formed a iine conductive screen orgrid 40 of between 500 and 700 mesh per inch.

y tained at a potential between 50 and 100 volts negative to groundpotential.

Adjacent to the target 12 on the reading side of the target there ismounted a screen electrode 48, which during tube operation is maintainedslightly positive with respect to the accelerating electrode coating 36to repel positive gas ions passing down the tube toward the target andwhich would discharge the negative charge pattern established in thetarget. As indicated in Figure l, screen 48 may be maintained across asupporting ring 50 which is sealed through the envelope wall 10 toprovide an external terminal for the screen electrode 48. The electronbeam 20 passing through screen 48 enters an intense retarding ordecelerating field between the screen electrodes 48 and 40. Screen 48provides a uniformity of decelerating iield over the adjacent surface ofthe target 12.

During tube operation, the electron beam 20 is magnetically scanned overthe adjacent surface of target 12 by fields provided by two pairs ofscanning coils indicated in Figure 1 by the deection yoke 52. Thedeflection yoke is of a conventional design, and as is well-known, eachpair of coils are connected respectively in series with each other tosources of sawtooth currents 54 and 56 for respectively providing frameand line scansion of beam 20 over the target surface.

The electron beam between the screen electrodes 48 and 40 is slowed downto a very low velocity so that it will strike the target electrode 12with an energy If the dielectric sheet 14 is mica, screen 40 may be toexpose the mica surface not covered by the masking screen. Upon removingof the masking screen there remains on the mica surface, portions of theoriginal metal coating in the form of a screen network. This method isdescribed in detail in the copending application of Harold B. Law,Serial Number 218,797, filed April 2, 1951, now Patent No. 2,702,274,and assigned to the same assignee as the present invention.

However, if the dielectric sheet 14 is a film of glass, the target hasbeen formed by stretching a line mesh nickel screen across a mountingring 42. A bubble of glass is blown until the glass is of the correctthickness in the order of 0.1 millas determined by counting theabsorption lines in the spectrum of reflected white light. A portion ofthe bubble is then laid over the mounting ring 42 which is thensubjected to a high temperature and in a nonoxidizing atmosphere untilthe glass of the bubble softens and lays down over the mesh screen 40.At the elevated temperature, the glass will seal to the metal screen andalso the screen 40 will become fused to the mounting ring 42. Theassembly is then cooled slowly to the freezing point of the glass.Since, the heat capacity of the glass is less than that of the metal,the assembly is cooled in the order of 100 C. per hour initiallyfollowed by a cooling of around 500 C. per hour to room temperature.

` As indicated in Figure 1, the fine mesh screen 40 is connected to asource of potential, which is substantially three volts positiverelative to ground or cathode potential of gun 18. Closely spaced, inthe order of from ve mils from the dielectric sheet 14 there is mountedon the writing gun side of target 12 a second fine mesh screen of only afew volts. The energy of the beam electrons is under these conditionsbelow that required for initiating secondary electron emission fromeither the reading screen 40 or the dielectric surface of iilm 14. Whenthe writing gun 16 is turned olf, the electrons of beam 20 approachingportions of the positive reading screen 40 will be collected thereby andconducted away. However, the electrons of beam 20 landing on theinsulating surfaces of film 14 will drive the dielectric surface of film14 negatively toward gun cathode potential, at which point the remainingelectrons of the beam are reilected as a return beam 58 back toward thereading gun 18. This condition is schematically shown in portion (a) ofFigure 3. The return beam 58 has less beam current than the incidentbeam 20 due to the collection of beam electrons by the positive readingscreen 40. The return beam 58 passes down the tube envelope 10 andstrikes a dynode surface 60, which is a portion of the iirstaccelerating electrode 34 of gun 18.

The electrons of the return beam 58 strike the dynode surface 60 withenergies sufficiently great to initiate a secondary emission therefrom,which is directed by a persuader electrode 62 into an electronmultiplier section 64 of the type disclosed in U. S. Patent 2,433,941 toPaul K. Weimer. The electrons are multiplied through several stages andfinally collected by the multiplier anode electrode 66 to provide anoutput signal in the circuit 68 of anode 66. A charge patterncorresponding to signals to be stored is established on the surface ofthe dielectric sheet 14 facing the writing gun 16. The incoming signalsmay be from any source such as, for example, those produced by thereception of reflected radar signals. These signals are appliedbetween'the control grid 24 and cathode 22 of the Writing gun 16, whichis connected in a circuit with a tube 70 for driving the control grid24. The signals thus applied to gun 16 modulate the electron beam 27 asit is scanned over the surface of target 12. As mentioned above thescansion of beam 27 may be a radar P. P. I. pattern by coupling thedeflection yoke 32 tothe movement of the radar antenna, as is wellknown.

The electron beam 27 will strike the dielectric target sheet 14 atenergies suflciently great to initiate a secondary emission' from thetarget surface greater than the primary beam current. However, ,sincethe writing screen 44 is held at around 100 volts negative relative toground potential theA Secondary electrons will be readily Ysuppressedand driven back to lthe target lm 14, thus, driving that point of thetarget surface negatively to ground. The current of beam 27 ismaintained at a smallvalue, so that, as the beam is scanned, from pointto point, the target surface will be driven negatively in the order ofrive volts for the maximum beam current. Since beam 27 is modulated,other portions of the target will be struck by less than the maximumbeam current and will be drivennegatively to a :correspondingly lessdegree.

When the `dielectric target sheet 14 is driven negatively by thewriting'beam 27 and to a potential something less than the maximum 5volts, the zero equipotential surfaces, which, before the writing .beamwas turned on, were in the surface of dielectric sheet 14, now emerge onthe reading side of the target and extend outwardly through the openingsof mesh 40. This is schematically shown in Figure 3(5). Thesezeroequipotential surfaces cut down'the area through which the electrons canenter to land ori the conductive collector mesh 40. When the dielectricsheet is driven more negatively, at any point by the writing beam 27,the zero equipotential surfaces now` spread out and overlap in thisparticular area and prevent any landing of the beam electrons on thecollector grid 40. This is schematically shown in Figure 3(c). n

As the insulator sheet 14 is driven negatively, the reading beam currentlandingon the collector mesh 40 is correspondingly decreased, while thereected return beam current is correspondingly increased; Figure 4 showsthe relationship of the reading beam current collected by the readingscreen 40 to the charge potential established at any one point on thedielectric target 14 by the writing beam. Figure 4 indicates that forpositive voltages between 3.5 and 8, established on the reading lscreen40, thereading beam current collected by mesh 40 is inverselyproportional to the negative voltage established at anyone point "on theinsulator sheet 14 by the writing beam.

As set forth above, the modulated writing beam landing on any one spotof the target will drive that spot negatively by a valuebetweenl to 5volts. rl`he potential to which the spot is driven is limited by thecurrentvalue of the writing beam at that spot. However, if the spot ishit repeatedly, the charge accumulated on the target surface 14increases linearly.

Normal operation of the tube is that in which the collector screen 40 ismaintained at around 3 volts positive. This does not provide anexcessive dilerence of potential between the positive grid 40 on onesurface of the dielectric sheet and the negative charge patternestablished by the writing beam on the other surface. At low potentialdierences between the target surfaces, the charge pattern is stored onthe dielectric sheet for longer periods of time.

In general a charge pattern is established on the writing side of target12 as described above. The reading beam 20 in scanning the oppositesurface of target 12 provides a return beam 58 which is modulated inaccordance with the number of electrons collected by the positive grid40 and in accordance with the charge pattern established on the writingside of target 12. The modulated return beam 58 is amplied by passingthrough the multiplier section 64 and provides the output signal of thetube. If dilerent information is to be stored on the target surface theprevious information can be erased by setting the suppressor screen 44back to 0 potential-and scanning the whole target area with the writingbeam. This will drive the writing side of the dielectric side 14 to thepotential of the suppressor grid 44 and thus erase the previous chargepattern established on the target surface. Or, in a similar manner anygiven area of the target can be erased by set ning only that portion ofthe dielectric surface of sheet l 14 with the writing beam.

An application of the tube described above is that in which incomingradar signals are applied to the control grid 24 of writing gun. Thewriting beam 27 is scanned over the surface of target 12 with a radar P.P. l. pattern. For example such a pattern is one in which the beam 27sweeps from the center of the target radially outward in a 500micro-second sweep. The beam Z7 and the deection current of yoke 32 arecut oi for a second 500 microseconds. The beam then is turned on againand strikes the center of the target. In the third 500 microsecondperiod, the beam again is deflected from the center radially outward butalong a path which is at a small angle to the path traced on theprevious sweep. In this manner, the beam is scanned to provide 1000traces or sweeps per second. It takes approximately 6 seconds for thebeam to trace the 360 about the center point of the target and return toits original trace. This is the same time as that for one rotation ofthe radar antenna which sent out 1000 pulses per second. Each radarpulse is synchronized with the beginning of the start of each trace ofthe electron beam 27 from the center of the target 12. The radar pulsesreiie'cted back to the antenna from various objects provide additionalpulses during each 500 microsecond period which constitute the signalapplied to the control grid. These reflected pulses or signals modulatethe electron beam between the beginningof each trace and the 'end of thetrace at the edge of the target. The control grid 24 of the writing gunmay be biased negatively to cut orf the electron beam at all timesunless pulsed or driven positively by a radar signal sent to the controlgrid by the circuit of tube 70. In this manner then there is establishedon the Writing side of the dielectric target 14, a charge patterncorresponding to the radar picture obtained.

In the radar application described, it is necessary that, as the writingbeam 27 scans over a previous trace on the target 12, new information beput down on the target. This then requires that the previous informationput down on the same trace be erased before the beam traces over theline again. The erasure of any radar trace by the beam prior to asucceeding trace may be accomplished by any appropriate method whichwould erase the old pictureat or very close to the instant of writing,so that no trailing or integration eect occurs to distort the picture.

The tube described above mayalso be uesd'for storage purposes other thanradar application. For example, a single transient oscilloscope tracecan be put down on the target by the Writing gun and be viewed as longas desired by the reading gun.

, Often it is desired to write at extremely high speeds, such as forshort duration single transient signals, as found in oscilloscopepractice. In such cases, it is necessary to raise the writing beamvoltage in order to get more writing current density. The upper limit ofthe writing beam Voltage is set by the thickness of the dielectric sheet14. For thin iilms it is possible to rind voltages `such that the beampenetrates through and causes emission of secondary electrons from thefar side of the insulator sheet. Thus, at excessive voltage it may beimpossible to charge the insulator negative as is required for this typeof operation.

it is also possible to magnetically focus the writing beam by extendingthe focus coil 3S of the reading beam and using an orthicon deiectionyoke similar to 52 for the writing beam gun. This has the advantage inthat the writing beam will also land peipendicularly on the target. Thesame effect may be accomplished by electrostatic means. Perpendicularwriting has the advantage of preventing trouble in applications where itis desired to selectively erase and write at any point chosen by thedeflection system. With the kinescope type of deection for the writingbeam shown in Figure l, the change iu '7 writing screen potential fromwriting to erasingvalues, cause a deiiection of the beam spot due to theangle of approach of the writing beam-to the screen 44. Withperpendicular landing, this is prevented.

Where the writing gun is spaced at voltages above the second crossoverpotential of the dielectric target surface, it is possible to obtainerasure on the Writing side by the addition of a spray beam of electronsat a lower voltage or by operating the writing gun between iirst andsecond crossover potential, during the erasure time.

While certain specific embodiments have been illustrated and described,it will be understood that various changes and modifications may be madetherein without departing from the spirit and scope of the invention.

I claim:

l.. A charge storage device comprising, a target electrode including animperforate dielectric sheet of material, a conductive grid in contactwith one surface of said dielectric sheet and a foraminous electrodespaced from the other surface of said dielectric sheet, means forproviding a modulated electron bombardment of said other surface of saiddielectric sheet to provide a charge pattern thereon, an electron gunfor providing a beam of electrons to be scanned over said one surface ofsaid dielectric sheet, and an electrode for collecting beam electronsreturned from said dielectric sheet.

2. A charge storage device comprising, a target electrode including animperforate dielectric sheet, an electron gun means for scanning onesurface of said target sheet with a beam of low velocity electrons, aforaminous collector electrode in contact with said one surface of saiddielectric sheet, an electron suppressor electrode spaced from theopposite surface of said dielectric sheet, and

means spaced from said opposite surface for providing a modulatedelectron bombardment of said opposite surface.

3. A charge storage device comprising, a target electrode including animperforate dielectric sheet, an electron gun means for scanning onesurface of said target sheet with a beam of low velocity electrons, acollector screen mounted on said one surface of said dielectric sheet,an electron suppressor screen spaced from the opposite surface of saiddielectric sheet, means spaced from said opposite surface for providinga modulated bombardment of said opposite target surface, and an anodeelectrode spaced from said one target surface for collecting beamelectrons reflected from said target.

4. A charge storage device comprising, a target electrode including anelectron impermeable dielectric sheet, a first electron gun means forscanning one surface of said target sheet with a beam of low velocityelectrons,

a collector'screen mounted on said one surface of said dielectric sheet,a second electron Vgun spaced from said opposite surface for providing-ahigh velocity beam directed at said opposite target surface, and asuppressor screen mounted between said second gun and said oppositetarget surface.

5. A charge storage device comprising, a target electrode including anelectron impermeable -dielectric sheet having a resistivity in the rangebetween 1014 ohm cm. and about 101s ohmcm., an electron gun for scanningone surface of said dielectric sheet with a beam of low velocityelectrons, an electron collecting screen mounted in contact with saidone dielectric surface, means spaced from the opposite surface of saiddielectric sheet for providing high velocity electrons directed at saidopposite dielectric surface, a 4suppressor electrode between said meansand said opposite dielectric surface.

6. A lcharge storage device comprising, a target electrode including animperforate glass sheet having a resistivity between 1016 and 101a ohmcm., a rst electron gun for scanning onev surface of said glass sheetwith a beam of low velocity electrons, a collector screen mounted overand in contact with said one glass sheet surface, a second'electron gunfor directing a beam of high velocity electrons at the opposite surfaceof said glass sheet, an electron suppressor screen spaced from saidopposite glass sheet surface, and an anode electrode for collecting beamelectrons reflected from said first glass sheet surface.

7. A charge storage tube comprising, a target electrode including anelectron impermeable dielectric sheet having high resistivity, meansincluding a first electron gun for scanning one surface of saiddielectric sheet with a beam of low velocity electrons, a collectorscreen over and in contact with 'said one dielectric sheet surface,means including a second electron gun for scanning a beam of highvelocity electrons over the opposite surface of said dielectric sheet, asecondary electron suppressor screen spaced from said opposite surfaceof said dielectric sheet, said second electron gun including a controlgrid for modulating said highv velocity beam, and an anode electrode forcollecting electrons reflected from said one surface of said dielectricsheet.

References Cited in the le of this patent UNITEDl STATES PATENTS EpsteinApr. 17, 1951

